Keratin-Mediated Selective Inhibition in Proliferation and Selective Apoptosis of Keloid Fibroblasts

Keloids are pathological scars characterized by excessive proliferation of fibroblasts and abnormal extracellular matrix (ECM) accumulation, largely mediated by transforming growth factor-β1 (TGF-β1). Current therapeutic approaches often fail due to high recurrence and limited selectivity. Here, we investigate the potential of human hair-derived keratin (HK) as a biomaterial with selective anti-fibrotic activity. Using multiple in vitro models including 2D monolayers, 3D spheroids, fibroblast-keratinocyte coculture, and collagen gel contraction, we evaluated the effects of 0.5% HK on keloid fibroblasts (KFs) and normal dermal fibroblasts (DFs), with and without TGF-β1 stimulation. HK selectively inhibited KF proliferation, viability, and migration while sparing DF. In 3D models, HK significantly reduced KF-mediated spheroid expansion and collagen matrix contraction, even under profibrotic stimulation. Mechanistically, HK activated intrinsic apoptotic signaling, up-regulating pro-apoptotic proteins (Bax, caspase-3, CYCS) and down-regulating Bcl-2 and XIAP. Transcriptomic profiling revealed that HK down-regulated pathways associated with ECM-receptor interaction, focal adhesion, and aminoacyl-tRNA biosynthesis in KF, suggesting a dual modulation of fibrotic remodeling and mitochondrial function. These findings demonstrate that HK exerts selective anti-fibrotic and pro-apoptotic effects on pathological fibroblasts, with minimal impact on normal cells. By modulating both ECM organization and cell survival pathways, keratin demonstrates strong potential as a therapeutic biomaterial for targeted keloid treatment.